Electron discharge apparatus



April 12, 1938. A. M. SKELLETT ELECTRON DISCHARGE APPARATUS Filed July21, 1956 ineman .325

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INVENTOR A. M SKELLETT Mam/v 6.7M

A TTORNE V l atented A r. 12, 1933 5 a I A z14"035 UNl'-l-ED STATESPATENT OFFICE.

ELECTRON DISCHARGE APPARATUS Albert M. Skellett, Madison, N. .I.,assignor to Bell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York Application July 21, 1936,Serial No. 91,652

' 13 Claims. (01. zso-z'u This invention .relates to electron dischargeapat high velocities and, therefore, secondary elecparatus and moreparticularly to such apparatus trons will be released from the anode.The greatincluding an electron discharge device and whereer portion ofthese secondary electrons will be in the space current of the device iscontrolled attracted to the third electrode or grid because 5byamagnetic field. of the potential difference between this elec- 5 5 Asis known in the art, the flow of electrons trode and the anode. Thecurrent 'which will between electrodes, for example between an inflow inan output or utilization circuit connected candescible cathode and ananode, of an electron between thev cathode and anode will bedeterdischarge device may be controlled by magnetic mined by thealgebraic sum of the primary elecfields which, for example may alter thepaths trons reaching the anode from the cathode and 10 I traversed bythe electrons or be of sufllcient inthe secondary electrons'fiowlng fromthe anode tensity to prevent electrons emanating from the to the thirdelectrode or grid.

cathode, from reaching the anode. Because of In accordance with onefeature of this inventhe high potential differences between theelection, the potentials upon the anode and the third trodes employed ingeneral at the present time, electrode or grid are so adjusted that there- 15 magnetic control of the space currentheretofore sultant anodecurrent is substantiallyzero or of i has necessitated the utilization ofvery intense a small fixed value and the anode current is then magneticfields and hence required the employvaried by a magnetic field of anintensity sufiiment of expensive magnetic structures. Furcient to affectappreciably only the secondary thermore, because of the great energy ofelectrons electrons released from the anode. More specifi- 20 emanatingfrom a cathode under the influence of cally, the potentials upon theanode and the third the high potential upon the anode, the sensitivityelectrode or grid are so adjusted that for each of the magnetic controlof the space current has primary electron reaching the anode from the Inot been as great asisdesired. a cathode a secondary electron from theanode One object 01'- this' invention ist'oenable highly flows to thethird electrode or grid. A variable 5 sensitive magnetic control of thespace current in' magnetic field is then produced adjacent and electrondischarge devices. 1 1 substantially parallel to the surface of theanode Another object of this invention is to enable directed towardthe'cathode. This field aflects the control of large space currents inhigh voltage only the secondary electrons and alters the orbits electrondischarge devices by a relatively weak thereof so that a portion ofthese electrons returns 3 magnetic field. to the anode instead offlowing to the third elec- A further object of this invention is toreduce trod'e or grid. Consequently, the equilibrium bethe cost and toincrease the efliciency of electron tween the primary and secondaryelectron cur-- discharge apparatus including electron discharge rents isdisturbed and a current will obtain in an devices wherein the spacecurrent is controlled output or utilization circuit connected to the 35by magnetic fields. cathode and the anode.

In one illustrative embodiment of this inven- Inasmuch as the secondaryelectrons leave'the tion, electron discharge apparatus comprises ananode with energies of but a fraction of a volt, electron dischargedevice including an incandescionly a weak magnetic field is necessaryto'affect 40 ble cathode, an anode and a third or grid electrode themand cause their return to the anode. Hence, 40 disposed between thecathode and anode, the surit will be apparent that such a weak field maybe face of the anode directed toward the cathode utilized to control avery large space current to preferably having a coating of a material;such as the anode, that is, a current composed of primary barium orcaesium oxide, which is an efilcient electrons. I

emitter of secondary electrons. The anode is The invention and thevarious features thereof 45 maintained at a high positive potential withrewill be understood more clearly and fully from spect to the cathodeand the third electrode or the following detailed description withreference grid likewise is maintained at a high positive to theaccompanying drawing in which: potential, greater than the anodepotential, with Fig. 1 is a view partly in perspective and partlyrespect to the cathode. diagrammatic of electron discharge apparatus 50In the operation of the apparatus, because of illustrative of oneembodiment of this invention, the high potentials upon the anode and thegri portions of the apparatus being broken away to alarge primaryelectron current will fiow from show the electron discharge device andthe electhe cathode to the anode. .I'he electrons constitrodes thereofmore clearly; f I

tuting this current will impinge upon theanode Fig. 2 is a graphillustrating the relationship 55 Figs. 4 and; are schematic views of anamplifier and an oscillator, respectively, embodying this invention; and

Fig. 6 is another schematic view illustrating the utilization of thisinventionin a modulator.

Referring now to the drawing, the apparatus shown in Fig. 1 comprises anenclosing vessel having a cylindrical body or central portion l andreduced end portions land l2 provided with inwardly extending stems l3and M respectively. Disposed within the enclosing vessel, and preferablycoaxial therewith, is an incandescible cathode l5, which may be of anyof the types known in the art. In the specific form shown in Fig. 1,

the cathode is 'a U-shaped filament supportedfrom the stem l3 byleading-in conductors l6 through which the cathode heating current froma source, such as a battery i1, is supplied.

The cathode l is encompassed by a cylindrical grid l8, preferablycoaxial with the cathode,

which is provided with a leading-in conductor l9 sealed in the stem M.The grid l8 in turn is encompassed by a cylindrical anode 20, preferablycoaxial therewith, having a. leading-in conductor 2| also sealed in thestem l4. Preferably the inner surface of the anode 20 is coated with amaterial which is an efiicient emitter of secondary electrons. Forexample, this surface may be coated with a monatomic layer of barium ora layer of caesium oxide.

The leading-in conductors l9 and 2| for the grid l8 and anode 20,respectively, are connected to suitable positive terminals of a source,such as a battery 22, the negative terminal of which is connected to thecathode I 5, the potential applied'to the grid I8 being greater thanthat applied to the anode 20. The primary winding 23 of an outputtransformer T1 may be connected between the battery 22 and the anode 26as shown.

The electron discharge device may be mounted between the arms 24 of amagnetic yoke, the arms being provided with suitable apertures forreceiving the end portions II and I2 of the encloing vessel of thedevice. The magnetic yoke may be composed of separable halves, heldtogether as by a screw 65 passing through a sleeve 46, to 7 allowpositioning of the electron discharge device with respect thereto.Preferably the opposed faces of the arms 24 are provided with annularprotuberances 25 of substantially the same diameter as the anode 20whereby concentratedmagnetic fields are produced adjacent the innersurface of the anode and substantially parallel thereto.

A portion of the magnetic yoke is encompassed by a field coil 26 throughthe agency of which the intensity of the magnetic fields extant adjacentthe anode may be varied. For example, the field coil 26 may be energizedfrom a circuit including the secondary winding 21 of an inputtransformer T2.

With suitable potentials upon the anode 20 and grid I 8, for example,potentials of several hundred volts, and the field coil 26 deenerg'ized,electronsemanating from the cathode l5 will travel toward the grid andanode at high velocities. Because of these velocities and the open-workcharacter of the grid, a large proportion of these primary electronswill reach and impinge upon the anode 20. These primary electrons uponstriking the anode cause the release of secondary electrons from theanode, some of which will flow to the grid l8, because of its higherpositive potential, and others of which will return to the anode 26. Thenet anode current, then, and hence the current flowing in the primarywinding 23 of the output transformer T1 will be the algebraic sum of thecurrent due to the primary electrons reaching the anode and the reversecurrent due to those secondary electrons which flow from the anode tothe grid. The magnitude of this net or resultant current will bedependent, of course, upon the difference of potential existing betweenthe anode and the grid.

'If the potentials upon the grid i8 and the anode 20 are properlyadjusted, a state of equilibrium will be established between the primaryand secondary electron currents so that the resultant current issubstantially zero. That is to say, the anode and grid potentials may beso adjusted that for each primary electron reaching the anode from thecathode, one electron will be released from-the anode and flow to thegrid. This state of equilibrium may be disturbed by energizing the fieldcoil 26 so that a magnetic field is'established adjacent the innersurface of the anode 20 and parallel thereto. This field, which shouldbe of such intensity that it does not affect appreciably the primaryelectron streams, will alter the orbits of a, portion or all of thesecondary electrons so that they will return to the anode and not passto the grid. Hence, an increase in the anode current results, themagnitude of this increase being dependent, upon the intensity of themagnetic field produced. By varying the intensity of this field, as byenergizing the coil 26 by a variable current, corresponding variationsin the output circuit will be obtained.

The relationship between the output current. which it may be noted iscomposed entirely of primary electrons, and the strength or intensity ofthe magnetic field is illustrated graphically in Fig. 2. As indicated inthis figure, when the magnetic field is zero and the state ofequilibrium between primary and secondary electrons heretofore mentionedobtains, the anode current is zero. When the magnetic field is produced,the anode current rises or increases rapidly as indicated by the portionAB of the curve. A further increase in the magnetic field produces but aslight .and gradual increase in the anode current as indicated by theportion B0 of the curve. If the magnetic field is increased stillfurther, it becomes of sufilcient intensity to affect the primaryelectrons and to prevent a portion of these electrons from reaching theanode, so that the anode current decreases as indicated by the portionCD of the curve.

It is desirable, of course, that during operation of the electrondischarge apparatus, the variations in the energizing current for thefield coil 26 correspond to the variations in the field intensity inturn corresponding to the portion AB of the curve in Fig. 2. Under suchconditions, it will be apparent that relatively large changes in theanode current may be produced by comparatively small variations in thefield intensity.

Hence, the electron discharge apparatus con enables the facile andeconomic control by elec- 7 tromagnetic means of relatively lai'gecurrents; that is to say, high potentials may be utilized upon the anode20 and grid l8 so that a large space current will fiow and the cathode I5 may be operated this figure, the magnetic yoke is provided with anelongated opening or slot 28 through which a magnetic tape 29 may bepassed. .As'the tape 29 is drawn through the opening or slot 28, the reluctance of the magnetic circuit is varied in accordance with variationsin the thickness of the tape or variations in the magnetization thereofand, hence, corresponding variations in the anode or output currentresult.

The variations in the magnetic field may be produced directly by a coilencompassing the electron discharge device or disposed in proximity tothe anode thereof. For example, in an amplifier such as illustrated inFig. 4, a coil 30 connected to an input circuit may be disposed inproximity to the anode 20 to produce a variable magnetic field ad--jacent and substantially parallel to the inner surface of the anode 20.Current variations corresponding to variations in the input current tothe coil 30 will thus be produced in the output transformer T1.

The invention may be utilized also in an oscillator, such asillustrated, for example, in Fig. 5. As shown in this figure, anoscillating coil 3| is connected between the grid l8 and anode 20 and inseries with a resistance 32 across which conductors 33 leading to anoutput or utilization circuit are connected. The coil 3| mayencompassthe enclosing vessel of the device or maybe disposed substantially inalignment with the anode 20. In shunt with the coil 3| is a variablecondenser 36 which may be adjusted to cause the generation ofoscillationsof a desired frequency.

The points upon the portion AB of the anode current-magnetic fieldcharacteristic at which the electron discharge device is to be operatedmay be determined by an auxiliary or biasing coil 34 disposed adjacentthe oscillating coil 3| and energized by a constant current from asource such as a battery 35, or may be determined by utilizing a yokesimilar to that shown in Figs. 1 and 2 and permanently magnetized toproduce a constant magnetic field of the requisite intensity. Preferablythe coils 3| and 34 are so wound and disposed that the magnetic fieldsproduced thereby are in opposition.

The auxiliary or biasing magnetic field may be produced alternately bythe anode 20 and the use of the auxiliary coil 34 thereby obviated. Forexample, the anode may be of a suitable ironnickel-aluminum alloy andpermanently magnetized to produce a permanent magnetic field 6, whereinthere is shown an electron discharge device including in addition to thecathode I 5,

anode 20 and grid I8, a second grid 31 disposed between the cathode l5and grid I8. The grid 31 may be biased negatively with respect to thecathode l5, as by a battery 39, through a connection including a seriesresistance 38 to the ends of which conductors 40 are connected. Asuitable current, for example of carrier frequency, may be suppliedthrough the conductors 40, in accordance with which the grid 31 variesthe primary electron anode current. A second current of modulatingfrequency is supplied to the coil 30 whereby -corresponding variationsin the anode current are producedby aifecting the secondary electroncurrent fromthe anode. The portion of the anode current-magnetic fieldcharacteristic upon which the device is to be operated may bedetermined, as heretofore described, by an auxiliary magnetic fieldproduced by either an auxiliary coil, by the anode 20, or by apermanently magnetized yoke.

Although specific embodiments of the invention have been shown anddescribed, it will be understood, of course, that these embodiments arebut illustrative of the invention and that various modifications may bemade therein without de-' parting from the scope and spirit of thisinvention as defined in the appended claims. ample, it may be desirablein some instances to utilize a permanently magnetized anode in theembodiments of the invention illustrated in Figs. 1, 3 and 4 as well asin those shown in Figs. 5 and 6.

What is claimed is:

1-. The method of controlling space current in an electron dischargedevice having a cathode, an anode capable of emitting secondaryelectrons and a grid between the cathode and anode, which comprisesapplying such positive potentials to said anode and grid that thesecondary electrons leaving said anode are substantially equal to the Isaid field being of sufificientintensity to affect only said secondaryelectrons.

2. The method of controlling space current in an electron dischargedevice having a cathode, an

anode adapted to emit secondary electrons and a grid between the cathodeand anode, which comprises applying positive potentials to said anodeand grid such that the primary electron current to said anode from saidcathode and the secondary electron current from said anode to said gridare substantially equal, producing a constant magnetic field adjacentsaid anode to decreasesaid secondary electron current, and producing avariable magnetic field adjacent said anode to vary said secondaryelectron current.

3. The method of controlling the output current of an electron dischargedevice including a cathode, an anode and a grid, which comprisesapplying such positive potentials to the grid and anode that a primaryelectron current flows to said anode from said cathode and a secondaryelectron current fiows to said grid from said anode, varying saidprimary current periodically to produce corresponding variations in theoutput current of said device, and simultaneously producing a variablemagnetic field adjacent said anode of sufiicient intensity to affectonly said secondary electron current.

4. Electron discharge apparatus comprising a cathode, a cylindrical gridencompassing said cathode, a cylindrical anode encompassing said grid,the surface of said anode directed toward said grid being adapted toemit secondary electrons, means applying positive potentials to saidanode and said grid with reference to said cathode, the potential onsaid grid being greater than that upon said anode and said potentialsbeing such that the secondary electrons released from said surface andflowing to said grid are substantially equal to the primary electronsflowing to said anode from said cathode, and means for producing avariable magnetic field adjacent and substantially parallel to saidsurface, said field being of sufficient intensity to affect only saidrial, means maintaining said grid and anode ata positive potential withrespect to said cathode such that the secondary electrons flowing fromsaid anode to said grid are substantially equal to the primary electronsflowing to said anode from said cathode, and means for producing avariable magnetic field immediately adjacent said surface andsubstantially parallel thereto.

6. Electron discharge apparatus comprising an enclosing vessel housing acathode, an anode, and agrid, means maintaining said grid and anode atpositive potentials with respect to said cathode, said potentials beingsuch that the primary electron current to said anode and the secondaryelectron current from said anode are substantially in equilibrium, amagnetic member having arms overlying opposite 1 edges of said anode,and means for varying the magnetic field produced by said magneticmember.

7. Electron discharge apparatus comprising an enclosing vessel housing acathode, a cylindrical anode encompassing said cathode and a cylindricalgrid between said cathg e ,and said anode, the inner surface of saidarid eibeing adapted to emit secondary electrons, means for applyingsuch positive potentials to said grid and said anode that the secondaryelectrons leaving said anode and the primary electrons reaching saidanode are substantially equal, means producing 'a concentrated magneticfield adjacent and substantially parallel to said surface including amagnetic yoke having arms overlying opposite 'ends of said anode, andmeans for varying the intensity of said field, said fields being ofsufilcient intensity to affect appreciably only the secondary electronsemanating from said surface.

8. Electron discharge apparatus comprising a cathode, an anode, a gridbetween said anode and cathode, and means for applying a positivepotential to said anode with respect to said cathode and a higherpositive potential to said grid, said anode being magnetized to producea magnetic field substantially parallel to the surface thereof towardsaid cathode.

9. Electron discharge apparatus comprising a cathode, an anode, and agrid between said cathode and said anode, the inner surface of saidanode being capable of emitting secondary electrons and said anode beingmagnetized to produce a magnetic field adjacent and substantiallyparallel to said surface, means applying a positive'potential to saidanode with respect to said cathode and for applying a higher positivepotential to said grid, and means for producing a variable magneticfield adjacent and-substantially parallel to said surface.

10. Electron discharge apparatus comprising a cathode, an anode, a grid,means maintaining said grid and anode at such positive potentials withrespect to saidcathode that the primary electron current to said anodeis substantially equal to the secondary electron current from saidanode, a coil for producing a substantially constant magnetic fieldadjacent said anode, and an oscillating coil connected in circuit withsaid anode and said grid for producing a variable magnetic fieldadjacent said anode.

11. Electron discharge apparatus in accordance with claim 10 whereinsaid coils are so related that the magnetic fields produced thereby arein opposition.

12. Electron discharge apparatus comprising a cathode, a grid, an anode,means for applying positive potentials to said grid and anode withrespect to said cathode whereby primary electrons fiow to said anodefrom said cathode and secondary electrons flow from said anode to saidgrid, means for varying the primary electron current flowing to saidanode, and means for producing a variablemagnetic field adjacent saidanode to vary the secondary electron current 'fiowing from said anode tosaid grid.

13. Electron discharge apparatus comprising a cathode, an anode, a gridbetween said cathode and said anode, a second grid between said cathodeand said first grid, means for applying posi tive potentials to saidanode and said first grid whereby a primary electron current flows fromsaid cathode to said anode and a secondary electron current fiows fromsaid anode to said first grid, means for applying a variable potentialbetween said cathode and said second grid to vary said primary current,and means for producing a variable magnetic field adjacent said anode,said field being of an intensity suflicient to materially affect onlysaid secondary electron current.

ALBERT M. SKELLE'I'I.

